This invention relates to an improved ceramic fiber molding and the method of making the same.
Ceramic fiber moldings are formed into many shapes and used for many purposes, generally moldings are used as furnace lining in the form of plates, cylinders and furnace construction members such as burner blocks. Presently, such ceramic fiber moldings are produced by dispersing and suspending the fibers in a large amount of water together with a binder such as colloidal silica and colloidal alumina. The suspended cermic fibers are collected by filtering to form the desired shape by either wet pressing or vacuum forming. Ceramic fibers for such purposes include aluminosilicate fiber and high alumina fibers. The aluminosilicate fiber is produced by blowing or spinning a melt consisting of 43 to 57 wt% of silica, 43 to 57 wt% of alumina, and less than 3 wt% of metal oxides or impurities. The high alumina fiber is produced by spinning a viscous solution of salts consisting of 3 to 20 wt% of silica, 80 to 97 wt% of alumina, and less than 1 wt% of other metal oxides, and subsequently converting the spun fibers into polycrystals of oxides by heating.
It is known that when chromium oxide, in an amount of 0.5 to 10 weight percent is incorporated into the ceramic fiber composition or chemically attached to the fiber surface the heat resistance of the cermic fiber is improved. However, the method of making aluminosilicate fiber by blowing or spinning a melt has the disadvantage in that the addition of chromium oxide to the composition changes the properties of the composition, particularly the viscosity of the melt, to such an extent that it is difficult to control the blowing or spinning of the fibers. On the other hand, the method of chemically attaching the chromium oxide to the fiber surface has a shortcoming in that the chromium oxide attached to the fiber surface evaporates within a short period of time when exposed to high temperatures.
The present invention discloses a method which prevents the chromium oxide from evaporating at high temperatures when ceramic fiber moldings are impregnated with chromium oxides. This method limits shrinkage and corrosion of the ceramic fiber moldings.
The process characterizing the present invention comprises dipping a ceramic fiber molding into a suspension containing either or both colloidal silica and colloidal alumina, in an amount of 0.2 to 1.0 wt% as solids based on the weight of the water of the suspension, and containing chromium oxide powder having a particle diameter smaller than 62 microns in an amount less than 30 wt% based on the weight of the water of the suspension, thereby impregnating said alumina-silica ceramic fiber molding with chromium oxide powder in an amount of 10 to 50 wt% based on the weight of the undipped ceramic fiber molding.
It is an object of this invention to produce ceramic fiber moldings which exhibit improved resistance to linear shrinking.
It is the further object of this invention to produce a ceramic fiber molding which is corrosion resistant.